I don't know what "Alcohol" is (in this context!!!), but if it assigns a drive letter, you should still be able to change that letter to a different, currently unused letter. I believe that in the Disk Management section you can lock a letter to a particular drive so that it won't get changed if you add other drives. I know I have done this in the past so that my DVD drives don't change letters when I add a new external drive (I'm now up to "Q:" ).
Alcohol is a program that creates a virtual CD drive and lets you copy a full working copy of any CD/DVD onto your hard drive for the sake of backups and performance increases (in some cases).
I've never used the program but have heard of it numerous times as the best of it's kind. I would imagine there should be a way to set a custom drive letter for Alcohol in the preferences.